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Discussion Starter #1
This a branch of the following thread about why new Hyundais are being built without ISG...I wanted to

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I'm not convinced stop/start actually does anything to improve air quality. And 10% of nothing is nothing.
https://carfromjapan.com/article/car-maintenance/how-much-gas-does-idling-use/

This article seems to suggest that idling an average car would use 0.75L of petrol per hour which makes sense. That equates to the about 0.025L of petrol for 2mins idling (the time at a fairly long red light).

On a motorway or long distance drive with few stops at lights the fuel savings and the total savings in air quality would be negligible.

However in a town...and in a very busy city centre like Brighton (where I live) you might have nine red lights in a 1.5km single stretch of road (a real life scenario near me, Preston Park to Elm Grove). Three of those are pedestrian crossings but the remaining six are full junctions where the full wait time is between 45s and 90s. Today I made that journey and got the stopwatch out! I was stationary four times for a total of 3mins (rush hour had been and gone)

So I used around 0.0375L of fuel idling alone along this single stretch of road alone.

Compare that to the amount of fuel used when driving and idling normally along the stretch of 1.5km at 35mpg you will use around 0.09L of fuel.

You could save 0.0375L of petrol for this stretch of road and therefore 42% less fuel and of course 42% less pollution.

Of course for a journey of 1hr going from town to town a stretch of road like this is not very common and in total fuel savings you may save 1% of fuel (which would be so very difficult to notice the difference on your mpg even though it may be there...but all these things add up over time and in different situations; like tyre pressure for instance being important for long distance mpg).

My point (and I honestly think I am correct here) is that for stretches of road like this, the savings in emissions would be very much significant.

42% less pollution on a road like this (maybe my calculations are really bad but even a 10% reduction may help the most vulnerable who live along or walk regularly along a polluted stretch of road).

An important point to this is that these locations are likely to be where the greatest concentrations of people are. So, it is not a general 42% reduction; it is a very very important 42%...the 42% that matters the most; where there are large concentration of pedestrians.

Alternatively, if you then say for a taxi rank you have on average 10 cars idling (quite common in rush hour outside Brighton train station). That spot might have the equivalent air quality of a busy road (let me know if you'd like the calculations!)...but with no idling at all that air pollution hotspot could be entirely eradicated. Also, some of these areas are covered areas (like Brighton train station taxi rank) which could makes those spaces 2,3 or even 4 times worse in terms of pollution.

My conclusion can only be that for towns, taxi ranks, major junctions and high streets that in terms of pollution alone, stop start can significantly reduce pollution. I know it is unpopular with some car enthusiasts for various reasons but here we have had some residents who have been suffering greatly with their respiratory health and pollution is a known killer and I think there is potential that it can help. I don't want to exagerate or scare but just to realise that I think it could have some really effective air quality and therefore reduce serious diseases.

(of course hybrid cars might be a better solution but...I'm talking about start stop!)
 

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My point (and I honestly think I am correct here) is that for stretches of road like this, the savings in emissions would be very much significant.
Perhaps, but your calculations don't allow for the extra fuel that is injected everytime the engine restarts. Was there any mention of that in the article you provided the link for?
 

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Perhaps, but your calculations don't allow for the extra fuel that is injected everytime the engine restarts. Was there any mention of that in the article you provided the link for?
This is from folklore from the days when engines had carburettors at the end of a long manifold. It is not because the combustion chamber demands the fuel, it is because carburettors couldn't deliver the right amount.

I wonder whether anybody has looked at the effect of ISG on traffic light throughput. I have noted elsewhere that my i20 DCT takes a second to start moving. Whereas a car with torque converter without ISG responds instantly to driver input.
 

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Discussion Starter #4
Thanks Autospark, I have just looked at my figures again, I am just updating them now (I made a couple of other errors too so am adding more detail to my calculations!).
 

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Discussion Starter #5
your calculations don't allow for the extra fuel that is injected everytime the engine restarts
That article mentions 10 seconds but it is a bit vague. I searched around the internet and new cars seem to be somewhere around 3 seconds but of course this would differ on make and model.
 

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Discussion Starter #7
ok, I spent a little too long on this! but I'm getting a better picture of the truth I think. I have looked at the 44% pollution reduction at major junctions figure a number of times and I do feel it is mostly correct...crazy amount!

Generally idling will cause pollution in specific isolated areas and start stop technology could irradicate that pollution. Here I will concentrate not on the global impact of the pollutants but at the location where the pollution is released. The differing scenarios are important to how much of an effect start-stop / idling will have on air quality. The location affected by idling will of course determine what air quality affects. Taxi ranks, junctions, high streets, spaces outside schools, hospitals and other areas where cars often stop for longer than a few seconds. The longer you idle and the more cars there are, the more pollution you would create in that specific location. The number and type of person in the location where the idling is taking place would make a difference to how the air quality would affect people.
I present a few scenarios (a link at the bottom for my calculations)
A long journey with minimal stopping Here the savings on pollution would be negligible because the car would not be stopped idling for much time at all! Although of course the locations where the car does stop would be subject to fewer pollutants.
Major junction at 11:30am on a weekday (figures taken from Preston Circus Brighton) During a full cycle of all traffic lights going from red to green and back for all junctions, 69 cars passed during 112 seconds. The cars used an estimated 0.451L of petrol. During this time 32 cars waited for 30 seconds using 0.2L of petrol. Idling in this scenario is responsible for 44% of the fuel used and therefore I assume idling is responsible for 44% of the pollution. It is a place where pedestrians will wait at crossings, drivers will sit in their cars, cyclists will stop catching their breath and where pedestrians sometimes have alternative routes. 44% here is a huge and very significant number.
Single car waiting in a single spot In a car you would use around 0.75L of petrol per hour idling and you would change that single location from being pollution free to a place equal to a single lane road with regular traffic (1 car every 12 seconds)
A 1.5km stretch of road with 4 major junctions with traffic lights A single 1.5km stretch of road could have four major junctions in a busy city. A car stops twice for a combined total of 2 minutes. The car will use around 0.025L of petrol idling. Driving along this stretch of road would use around 0.15L of petrol, assuming the amount of fuel is equal to the pollution then start stop could reduce pollution by 6%. This is a fairly small amount compared to the total but it is still significant difference in the air quality along a large stretch of road. Streets like these in city centres will have many more people than in other areas waiting at the lights, walking along pavements, people working in shops, people living in flats above the roads, cyclists and drivers will be in their cars taking in the pollution. These areas are some of the most dangerous generally for people because of the number of people so 6% could make a significant difference.
A taxi rank A taxi rank with 10 cars idling in a space of around 35m. That 35m spot could have the air quality equal to a reasonably busy dual carriage way (a car every 1.68 seconds). Some taxi ranks are covered (such as those near train stations) which could make those spaces much much worse as the pollution would not be dispersed easily. There will be people waiting for taxis next to the taxi rank, people waiting nearby as taxi ranks are usually in busy locations and the taxi drivers themselves will be sitting directly in these toxic fumes so there will be many people exposed to this pollution. With start-stop, this pollution would be completely eradicated.
A school The cars could be spread out more so you could say it would be a half of the above, so a busy single lane A road maybe. The affects of pollution are greater on children because their lungs are smaller, more sensitive and growing. Children and babies in prams are also more affected because they are shorter and closer to the pollution.
https://docs.google.com/document/d/1rASB96LRIP1II4vkxGKncshfZpR3iNAy9ONmSHAkTGs/edit?usp=sharing
 

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Discussion Starter #8
I allowed 10 seconds for engine startup so the figures are probably underestimated in terms of start-stop being beneficial for pollution in certain scenarios. New cars as stated above are more like 2.5s
 

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Discussion Starter #9 (Edited)
Ha! I have seen that video before!!! The guy is not a scientist and probably did well in the used car business before he discovered Youtube to make his money. Please don't fall for that, I think my figures are mostly correct and pollution is a killer so should be treated with more respect and intelligence. Most of the complaints about the stop start tech is about fuel efficiency anyway, not about air quality (although it seems it is beneficial to fuel efficiency and idling is worse for your vehicle).

Here are some more links which are a bit more open to constructive criticism and review.



 

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Ha! I have seen that video before!!! The guy is not a scientist and probably did well in the used car business before he discovered Youtube to make his money.
He clearly isn't a scientist but he must have some knowledgeable people behind him; he communicates engineering aspects far better than most in the motor trade.
Most of the complaints about the stop start tech is about fuel efficiency anyway, not about air quality
The best way to improve air quality in towns would be to control the number of private cars.
And for people to reduce the large number of short car journeys that can be done on foot or bicycle (or electric bicycle). Of course, most people want a bigger SUV and that's something for others to do.

Here are some more links which are a bit more open to constructive criticism and review.
....
There's little science in those.

I love one of the comments "You aren't really giving any reasons why idling would be any worse than time spent driving. It's like saying "driving the car isn't good for the car""
 

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Discussion Starter #11
Yes, I agree about reducing car usage (I think that guy might explode if you tried to take his car away from him though!) It's been a tricky one to get owners to part from their cars but I think there is a chance new technology (machine learning, electric innovations, self driving can help...maybe). I spent a few days in Vilnius Lithuania a little while ago and they have electric scooters that get up to 25kmph; so much fun! In addition to my i10 I have a folding electric bike and that, coupled with a train can get me almost anywhere.

I picked stop-start because the tech is already there. I am so surprised though that 44% of the pollution at my local junction is due to cars idling! For health reasons I think that should be given a higher level of importance.

(yes, there are some bad posts there too I suppose but I think the science in my calculations is correct and there are some well referenced, calculated and thought out answers)

Not exactly the same but here is half a litre of petrol being burnt!
So, that would be the equivelent of 30 cars idling for a minute (minus the particulate filters of course...but the gases have to go somewhere).
 

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Discussion Starter #12
In summary I feel that stop-start can really save a lot of pollution in certain places and I am so surprised by how much. The main convincers for me are

1. the 44% saving of pollution at large junctions is massive and could really improve health in the most polluted public places
2. 0.2 seconds of idling is the cut off point between saving fuel and conserving fuel when switching the engine off (link)
3. idling is actually worse for the engine that restarting your engine (link)

Thanks all for the journey...now Hyundai...give the i10 stop-start!!!
 

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Discussion Starter #14
Letting my car idle will put additional stress on the engine simply because it is being used; more work equals more wear and tear. Also, your car is being pushed to its limit in terms of heat because there is less air passing through the engine (and if my fan is strong enough and working sufficiently then my car will use more fuel as it works harder). For proof just watch the number of cars that overheat on the hottest days of the year whilst in traffic jams and damage a whole load of components or listen to your fan kick into a higher speed.

The reason why we have some myths I think is because this problem is a scenario dependent one, it is possible to find one scenario that counters the arguments of another but, there are far more scenarios where letting our stop-start tech take over will be beneficial to the environment, other people we share the roads with, pedestrians, ourselves and our cars so...I think that is is why it is a general rule.
 

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I think if the ISG had a delay of ~10 seconds it would be a lot less annoying.
So stopping briefly at a stop sign, or parking maneuvers etc. wouldn't stop the engine.
But sitting at a long light or a traffic backup it would still activate.
 

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What about the part where the "parts" arent simply available and have to be manufactured from raw earth materials. Where does that carbon footprint go, where does the cost of that production go? Not even quid pro quo. Prove me wrong. You waste far more resources in replacement parts from the cycles used to shut down in whatever you want to in ad-----whatever you wanna spell it..
 

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Letting my car idle will put additional stress on the engine simply because it is being used; more work equals more wear and tear...

The reason why we have some myths I think is because this problem is a scenario dependent one...
I think we are arguing at cross purposes.

I believe stop-start is completely benign - neither harm nor benefit - just an occasional inconvenience. Most engines reach the scrapyard in perfect working order so reducing a bit of idling won't make the slightest difference. For people that don't waste their time driving in large towns and cities the fuel saving is zero. A modern engine, when idling, produces no pollution - only CO2 which has global effect but no effect on local air quality. The nasties are produced when accelerating.

But if people ask questions about whether starting takes more fuel than idling, it is no good posting links to articles that perpetuate the idea there is a time tradeoff. One reason we have myths is because technology changes but habits don't.
 
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